I am planning a Windows Server 2012 backup unit, and NAS backup could be a natural choice, however for safety reasons, the client will be forced to perform disk rotations, hence weekly the backup unit will be detached and NAS units aren't made for this as the connectors may get teared during time. So I thought about external USB portable disks (cheap solution nowadays) for backup and weekly rotation, however USB units may require console intervention on detachment to allow safe disconnection. I am aware of fast disconnection of disk units, but I wonder if this is safe, and if there could be a better solution for this task
Nah, it's safe. It's a synchronously mounted filesystem with a disabled on-disk write buffer (that's the only difference). Both of these are software controlled, and you can do this with any media. This is controlled in the drive properties within the device mangler.
I won't say this is a particularly terrible solution for the task, but it will be a bit more manual than a well-automated form of secure backup that does not use disk rotation and instead uses diff / incremental transportable snapshot rotation to disparate cloud resources.
However, since you're already having to do disk rotations, it won't actually be much more work. There are auto-loading disk systems out there that could do the job, but they're VERY expensive and generally pretty archaic.
Almost as archaic as manual disk rotations. But this will work in a small scale situation.
Don't go for USB backup with large amount of files - I unfortunately implemented this solution to backup >4TB data and >12000000 files to 5TB usb 3.0 drive... the I/O is so slow, that backup takes almost tree days (weekend).
here You have backup performance with usb disk an native sata:
About disconecting - I'm not sure what You are afraid for? just disable cache write on usb disk - this solves the possibility of data loss on disk unplug on idle (we are using 2 USB drive for rotating backup - on monday I just disconnectin drive, works like a charm)